A massive Multi-input Multi-output (MIMO) system attracts wide attention from the academia and the industry in recent years. The theoretical study shows that the massive MIMO system can significantly improve spectrum efficiency and energy efficiency of the system with simple linear detection and pre-coding algorithms, for example Zero Forcing (ZF) algorithm, Minimum Mean Square Error (MMSE) algorithm and the like, thus the massive MIMO is likely to be adopted as key technology for a next generation communication standard.
In an actual system, there are a series of problems to be solved in the massive MIMO technology. In theoretical study of the massive MIMO, generally it is assumed that a base station adopts a linear array with a uniform spacing, i.e., antennas are placed in only a horizontal direction. In a case that the number of antennas is great, the linear array will result in that an antenna scale of the base station is too large and is difficult to be realized. One of solutions to the problem is to adopt a 3D-MIMO system in which antennas are placed in both a horizontal direction and a vertical direction. For the 3D-MIMO system, degrees of freedom (related to the number of antennas in the horizontal direction and the vertical direction) in both the horizontal direction and the vertical direction can be utilized, thereby reducing the scale of the antenna array effectively. In addition, an extra degree of freedom in the vertical direction can be used to weaken interference between users and reduce interference between cells and so on, and hence the system performance can be improved to a certain degree. Due to these advantages, the 3D-MIMO technology attracts attention from the industry, and is likely to be incorporated into the existing wireless communication standard.
Since the user equipment has limited feedback accuracy, accurate channel status information can not be obtained using the existing channel estimation and feedback schemes, and the system performance can not be improved effectively.